U.S. patent number 10,578,046 [Application Number 16/092,831] was granted by the patent office on 2020-03-03 for fuel injection control device.
This patent grant is currently assigned to TOYOTA JIDOSHA KABUSHIKI KAISHA. The grantee listed for this patent is DENSO CORPORATION, TOYOTA JIDOSHA KABUSHIKI KAISHA. Invention is credited to Tomohiro Nakano, Nobuyuki Satake.
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United States Patent |
10,578,046 |
Satake , et al. |
March 3, 2020 |
Fuel injection control device
Abstract
A fuel injection control device has a detection unit, a
correction value calculation unit, and a conduction time
calculation unit. The detection unit detects a current increase
speed that is a speed of increasing an electric current flowing in
an electromagnetic coil in accordance with the start of conducting
the electromagnetic coil during partial lift injection in which a
valve body starts valve closing operation before the valve body
reaches a maximum valve opening position after the valve body
starts valve opening operation. The correction value calculation
unit calculates a correction value for a requested injection
quantity on the basis of the detected current increase speed. The
conduction time calculation unit calculates a conduction time of
the electromagnetic coil during the partial lift injection on the
basis of the requested injection quantity corrected by the
correction value.
Inventors: |
Satake; Nobuyuki (Kariya,
JP), Nakano; Tomohiro (Nagoya, JP) |
Applicant: |
Name |
City |
State |
Country |
Type |
TOYOTA JIDOSHA KABUSHIKI KAISHA
DENSO CORPORATION |
Aichi
Aichi |
N/A
N/A |
JP
JP |
|
|
Assignee: |
TOYOTA JIDOSHA KABUSHIKI KAISHA
(Toyota, JP)
|
Family
ID: |
60202906 |
Appl.
No.: |
16/092,831 |
Filed: |
April 7, 2017 |
PCT
Filed: |
April 07, 2017 |
PCT No.: |
PCT/JP2017/014476 |
371(c)(1),(2),(4) Date: |
October 11, 2018 |
PCT
Pub. No.: |
WO2017/191733 |
PCT
Pub. Date: |
November 09, 2017 |
Prior Publication Data
|
|
|
|
Document
Identifier |
Publication Date |
|
US 20190120167 A1 |
Apr 25, 2019 |
|
Foreign Application Priority Data
|
|
|
|
|
May 6, 2016 [JP] |
|
|
2016-093320 |
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
F02D
41/20 (20130101); F02D 41/3094 (20130101); F02D
41/345 (20130101); F02D 41/247 (20130101); F02M
51/061 (20130101); F02D 2041/389 (20130101); Y02T
10/44 (20130101); Y02T 10/40 (20130101); F02D
2041/2058 (20130101); F02D 2200/0614 (20130101); F02D
2041/2055 (20130101) |
Current International
Class: |
F02D
41/34 (20060101); F02D 41/24 (20060101); F02D
41/20 (20060101); F02D 41/30 (20060101); F02M
51/06 (20060101); F02D 41/38 (20060101) |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
|
|
|
|
|
|
|
2013/191267 |
|
Dec 2013 |
|
WO |
|
2017/191728 |
|
Nov 2017 |
|
WO |
|
2017/191729 |
|
Nov 2017 |
|
WO |
|
2017/191730 |
|
Nov 2017 |
|
WO |
|
2017/191731 |
|
Nov 2017 |
|
WO |
|
2017/191732 |
|
Nov 2017 |
|
WO |
|
Other References
Jun. 20, 2017 International Search Report issued in International
Patent Application No. PCT/JP2017/014476. cited by applicant .
Jun. 20, 2017 Written Opinion issued in International Patent
Application No. PCT/JP2017/014476. cited by applicant .
May 16, 2019 Office Action issued in European Patent Application
No. 17792666.4. cited by applicant.
|
Primary Examiner: Vo; Hieu T
Attorney, Agent or Firm: Oliff PLC
Claims
The invention claimed is:
1. A fuel injection control device that is applied to a fuel
injection valve including a valve body to open and close an
injection hole to inject a fuel and an electric actuator that has
an electromagnetic coil and a movable core to move by being
attracted by an electromagnetic force generated by conducting the
electromagnetic coil and operates the valve body for valve opening,
the fuel injection control device to control a valve opening time
of the valve body by controlling a conduction time of the
electromagnetic coil and thus control an injection quantity
injected per one time valve opening of the valve body, the fuel
injection control device comprising: a detection unit to detect a
current increase speed that is a speed of increasing an electric
current flowing in the electromagnetic coil in accordance with the
start of conducting the electromagnetic coil during partial lift
injection in which the valve body starts valve closing operation
before the valve body reaches a maximum valve opening position
after the valve body starts valve opening operation; a correction
value calculation unit to calculate a correction value for a
requested injection quantity that is the injection quantity
required on the basis of the current increase speed detected by the
detection unit; and a conduction time calculation unit to calculate
the conduction time of the electromagnetic coil during the partial
lift injection on the basis of the requested injection quantity
corrected by the correction value.
2. The fuel injection control device according to claim 1, wherein
the correction value calculation unit includes an offset correction
quantity calculation unit to calculate an offset correction
quantity to correct the requested injection quantity by adding the
offset correction quantity to or subtracting the offset correction
quantity from the requested injection quantity on the basis of the
current increase speed, and a correction coefficient calculation
unit to calculate a correction coefficient to correct the requested
injection quantity by multiplying the requested injection quantity
by the correction coefficient on the basis of the current increase
speed.
3. The fuel injection control device according to claim 2, wherein
an injection characteristic line representing a relationship
between the conduction time and the injection quantity in the
partial lift injection includes a first region where the
inclination of the injection characteristic line increases
gradually in proportion to the increase of the conduction time and
reaches a prescribed inclination, and a second region, the second
region being a region on the side where the conduction time is
longer than the first region, where the inclination of the
injection characteristic line forms a constant straight line, and
the correction coefficient calculation unit calculates the
correction coefficient on the basis of the inclination of the
injection characteristic line in the second region estimated from a
correlation with the current increase speed.
4. The fuel injection control device according to claim 2, wherein
an injection characteristic line representing a relationship
between the conduction time and the injection quantity in the
partial lift injection includes a first region where the
inclination of the injection characteristic line increases
gradually in proportion to the increase of the conduction time and
reaches a prescribed inclination, and a second region, the second
region being a region on the side where the conduction time is
longer than the first region, where the inclination of the
injection characteristic line forms a constant straight line, a
value of the conduction time when the injection quantity is zero on
a virtual straight line formed by extending the straight line is
defined as a virtual time, and the offset correction quantity
calculation unit calculates the offset correction quantity on the
basis of the virtual time estimated from a correlation with the
current increase speed.
5. The fuel injection control device according to claim 1, wherein
the detection unit obtains the current increase speed by detecting
a time required from the start of conducting the electromagnetic
coil until an electric current flowing in the electromagnetic coil
reaches a prescribed value.
Description
CROSS REFERENCE TO RELATED APPLICATION
This application is based on Japanese Patent Application No.
2016-93320 filed on May 6, 2016, the disclosure of which is
incorporated herein by reference.
TECHNICAL FIELD
The present disclosure relates to a fuel injection control device
to control an injection quantity of a fuel injected through a fuel
injection valve.
BACKGROUND ART
In Patent Literature 1, a fuel injection valve to inject a fuel by
operating a valve body for valve opening by an electromagnetic
force caused by conduction of an electromagnetic coil is disclosed.
Further, a fuel injection control device to control a valve opening
time of a valve body by controlling a time for energizing the
electromagnetic coil and thus control an injection quantity
injected per one time valve opening of the valve body is disclosed.
A conduction time is set at a time corresponding to an injection
quantity that is requested (requested injection quantity).
PRIOR ART LITERATURES
Patent Literature
Patent Literature 1: JP2015-96720A
SUMMARY OF INVENTION
Meanwhile, in recent years, the development of partial lift
injection (refer to Patent Literature 1) in which a valve body
starts valve closing operation before the valve body reaches a
maximum valve opening position after the valve body starts valve
opening operation advances. In the partial lift injection, since a
conduction time is extremely short, a period of time when valve
opening operation cannot start and a fuel is not injected (namely
invalid injection period) because an electromagnetic force is small
in spite of the fact that the period is immediately after the start
of the conduction and during the conduction accounts for a large
proportion of the conduction time. Consequently, in the partial
lift injection, an injection quantity varies largely only because
an invalid injection period varies slightly.
When the temperature of an electromagnetic coil varies however, the
electric resistance of the electromagnetic coil varies and hence
the speed of increasing the electric current flowing in the
electromagnetic coil (coil current) immediately after the start of
conduction also varies. As a result, an invalid injection period
varies, correspondence between a requested injection quantity and a
conduction time (namely injection characteristic) varies
undesirably, and a fuel injection quantity in partial lift
injection cannot be controlled with a high degree of accuracy.
An object of the present disclosure is to provide a fuel injection
control device that attempts to control a fuel injection quantity
in partial lift injection with a high degree of accuracy.
According to an aspect of the present disclosure, the fuel
injection control device is applied to a fuel injection valve
including a valve body to open and close an injection hole to
inject a fuel and an electric actuator that has an electromagnetic
coil and a movable core to move by being attracted by an
electromagnetic force generated by conducting the electromagnetic
coil and operates the valve body for valve opening, controls a
valve opening time of the valve body by controlling a conduction
time of the electromagnetic coil and thus control an injection
quantity injected per one time valve opening of the valve body. The
fuel injection control device includes a detection unit to detect a
current increase speed that is a speed of increasing an electric
current flowing in the electromagnetic coil in accordance with the
start of conducting the electromagnetic coil during partial lift
injection in which the valve body starts valve closing operation
before the valve body reaches a maximum valve opening position
after the valve body starts valve opening operation, a correction
value calculation unit to calculate a correction value for a
requested injection quantity that is the injection quantity
required on the basis of the current increase speed detected by the
detection unit, and a conduction time calculation unit to calculate
the conduction time of the electromagnetic coil during the partial
lift injection on the basis of the requested injection quantity
corrected by the correction value.
Meanwhile, a change of an injection characteristic responding to a
temperature has a high correlation with a speed at which an
electric current flowing in an electromagnetic coil increases in
accordance with the start of conducting the electromagnetic coil.
According to the above disclosure considering this point, during
partial lift injection, a speed at which an electric current
flowing in an electromagnetic coil increases is detected, a
correction value for a requested injection quantity is calculated
on the basis of the detected current increase speed, and the
requested injection quantity is corrected by the correction value.
As a result, during the partial lift injection, since an
electromagnetic coil can be controlled by a conduction time
suitable for an injection characteristic varying in response to a
temperature, a fuel injection quantity in the partial lift
injection can be controlled with a high degree of accuracy.
BRIEF DESCRIPTION OF DRAWINGS
The above and other objects, features and advantages of the present
disclosure will become more apparent from the following detailed
description made with reference to the accompanying drawings. In
the drawings:
FIG. 1 is a view showing a fuel injection system according to a
first embodiment;
FIG. 2 is a sectional view showing a fuel injection valve;
FIG. 3 is a graph showing a relationship between a conduction time
and an injection quantity;
FIG. 4 is a graph showing the behavior of a valve body;
FIG. 5 is a graph showing a relationship between a voltage and a
difference;
FIG. 6 is a graph for explaining a detection range;
FIG. 7 is a flowchart showing injection control processing;
FIG. 8 is a graph showing the variations of a coil current and an
injection rate with the lapse of time in partial injection and also
is a graph showing an example of the case where an injection
quantity decreases because an electric resistance increases by high
temperature;
FIG. 9 is a graph showing the variations of a coil current and an
injection rate with the lapse of time in partial injection and also
is a graph showing an example of the case where an injection
quantity increases because an electric resistance increases by high
temperature; and
FIG. 10 is a graph showing the variation of an injection
characteristic responding to temperature.
DESCRIPTION OF EMBODIMENTS
Embodiments of the present disclosure will be described hereafter
referring to drawings. In the embodiments, a part that corresponds
to a matter described in a preceding embodiment may be assigned
with the same reference numeral, and redundant explanation for the
part may be omitted. When only a part of a configuration is
described in an embodiment, another preceding embodiment may be
applied to the other parts of the configuration.
(First Embodiment)
A first embodiment according to the present disclosure is explained
in reference to FIGS. 1 to 10. A fuel injection system 100 shown in
FIG. 1 includes a plurality of fuel injection valves 10 and a fuel
injection control device 20. The fuel injection control device 20
controls the opening and closing of the fuel injection valves 10
and controls fuel injection into a combustion chamber 2 of an
internal combustion engine E. The fuel injection valves 10: are
installed in an internal combustion engine E of an ignition type,
for example a gasoline engine; and inject a fuel directly into a
plurality of combustion chambers 2 of the internal combustion
engine E respectively. A mounting hole 4 penetrating concentrically
with an axis C of a cylinder is formed in a cylinder head 3
constituting the combustion chamber 2. A fuel injection valve 10 is
inserted into and fixed to the mounting hole 4 so that the tip may
be exposed into the combustion chamber 2.
A fuel supplied to the fuel injection valve 10 is stored in a fuel
tank not shown in the figure. The fuel in the fuel tank is pumped
up by a low-pressure pump 41, the fuel pressure is raised by a
high-pressure pump 40, and the fuel is sent to a delivery pipe 30.
The high-pressure fuel in the delivery pipe 30 is distributed and
supplied to the fuel injection valve 10 of each cylinder. A spark
plug 6 is attached to a position of the cylinder head 3 facing the
combustion chamber 2. Further, the spark plug 6 is arranged in a
vicinity of the tip of the fuel injection valve 10.
The configuration of the fuel injection valve 10 is explained
hereunder in reference to FIG. 2. As shown in FIG. 2, the fuel
injection valve 10 includes a body 11, a valve body 12, an
electromagnetic coil 13, a stator core 14, a movable core 15, and a
housing 16. The body 11 comprises a magnetic material. A fuel
passage 11a is formed in the interior of the body 11.
Further, the valve body 12 is contained in the interior of the body
11. The valve body 12 comprises a metal material and is formed
cylindrically as a whole. The valve body 12 can be displaced
reciprocally in an axial direction in the interior of the body 11.
The body 11 is configured so as to have an injection hole body 17
in which a valve seat 17b where the valve body 12 is seated and an
injection hole 17a to inject a fuel are formed at the tip part. The
injection hole 17a includes a plurality of holes formed radially
from the inside toward the outside of the body 11. A fuel of a high
pressure is injected into the combustion chamber 2 through the
injection hole 17a.
The main body part of the valve body 12 has a columnar shape. The
tip part of the valve body 12 has a conical shape extending from
the tip of the main body part on the side of the injection hole 17a
toward the injection hole 17a. The part, which is seated on the
valve seat 17b, of the valve body 12 is a seat surface 12a. The
seat surface 12a is formed at the tip part of the valve body
12.
When the valve body 12 is operated for valve closing so as to seat
the seat surface 12a on the valve seat 17b, the fuel passage 11a is
closed and fuel injection from the injection hole 17a is stopped.
When the valve body 12 is operated for valve opening so as to
separate the seat surface 12a from the valve seat 17b, the fuel
passage 11a is open and a fuel is injected through the injection
hole 17a.
The electromagnetic coil 13 is an actuator and gives a magnetic
attraction force to the movable core 15 in a valve opening
direction. The electromagnetic coil 13 is configured by being wound
around a resin-made bobbin 13a and is sealed by the bobbin 13a and
a resin material 13b. In other words, a coil body of a cylindrical
shape includes the electromagnetic coil 13, the bobbin 13a, and the
resin material 13b. The bobbin 13a is inserted over the outer
peripheral surface of the body 11. The stator core 14 comprises a
magnetic material and is formed cylindrically and is fixed to the
body 11. A fuel passage 14a is formed in the interior of the
cylinder of the stator core 14.
Further, the outer peripheral surface of the resin material 13b to
seal the electromagnetic coil 13 is covered with the housing 16.
The housing 16 comprises a metallic magnetic material and is formed
cylindrically. A lid member 18 comprising a metallic magnetic
material is attached to an opening end part of the housing 16.
Consequently, the coil body is surrounded by the body 11, the
housing 16, and the lid member 18.
The movable core 15 is a mover and is retained by the valve body 12
relatively displaceably in the direction of driving the valve body
12. The movable core 15 comprises a metallic magnetic material, is
formed discoidally, and is inserted over the inner peripheral
surface of the body 11. The body 11, the valve body 12, the coil
body, the stator core 14, the movable core 15, and the housing 16
are arranged so that the center lines of them may coincide with
each other. Then the movable core 15 is arranged on the side of the
stator core 14 closer to the injection hole 17a and faces the
stator core 14 in the manner of having a prescribed gap from the
stator core 14 when the electromagnetic coil 13 is not
conducted.
The body 11, the housing 16, the lid member 18, and the stator core
14, which surround the coil body: comprise magnetic materials as
stated earlier; and hence form a magnetic circuit acting as a
pathway of a magnetic flux generated when the drive coil 13 is
conducted. Components such as the stator core 14, the movable core
15, the electromagnetic coil 13, and the like correspond to an
electric actuator EA to operate the valve body 12 for valve
opening.
As shown in FIG. 1, the outer peripheral surface of a part of the
body 11 located on the side closer to the injection hole 17a than
the housing 16 is in contact with an inner peripheral surface 4b of
the mounting hole 4 on the lower side. Further, the outer
peripheral surface of the housing 16 forms a gap from an inner
peripheral surface 4a of the mounting hole 4 on the upper side.
A through hole 15a is formed in the movable core 15 and, by
inserting the valve body 12 into the through hole 15a, the valve
body 12 is assembled to the movable core 15 slidably and relatively
movably. A locking part 12d formed by expanding the diameter from
the main body part is formed at an end part, which is located on
the upper side in FIG. 2, of the valve body 12 on the side opposite
to the injection hole. When the movable core 15 is attracted by the
stator core 14 and moves upward, the locking part 12d moves in the
state of being locked to the movable core 15 and hence the valve
body 12 also moves in response to the upward movement of the
movable core 15. Even in the state of bringing the movable core 15
into contact with the stator core 14, the valve body 12 can move
relatively to the movable core 15 and can lift up.
A main spring SP1 is arranged on the side of the valve body 12
opposite to the injection hole and a sub spring SP2 is arranged on
the side of the movable core 15 closer to the injection hole 17a.
The main spring SP1 and the sub spring SP2 are coil-shaped and
deform resiliently in an axial direction. A resilient force of the
main spring SP1 is given to the valve body 12 in the direction of
valve closing that is the downward direction in FIG. 2 as a counter
force coming from an adjustment pipe 101. A resilient force of the
sub spring SP2 is given to the movable core 15 in the direction of
attracting the movable core 15 as a counter force coming from a
recess 11b of the body 11.
In short, the valve body 12 is interposed between the main spring
SP1 and the valve seat 17b and the movable core 15 is interposed
between the sub spring SP2 and the locking part 12d. Then the
resilient force of the sub spring SP2 is transferred to the locking
part 12d through the movable core 15 and is given to the valve body
12 in the direction of valve opening. It can also be said therefore
that a resilient force obtained by subtracting a sub resilient
force from a main resilient force is given to the valve body 12 in
the direction of valve closing.
Here, the pressure of a fuel in the fuel passage 11a is applied to
the whole surface of the valve body 12 but a force of pushing the
valve body 12 toward the valve closing side is larger than a force
of pushing the valve body 12 toward the valve opening side. The
valve body 12 therefore is pushed by the fuel pressure in the
direction of valve closing. During valve closing, the fuel pressure
is not applied to the surface of a part of the valve body 12
located on the downstream side of the seat surface 12a. Then along
with valve opening, the pressure of a fuel flowing into the tip
part increases gradually and a force of pushing the tip part toward
valve opening side increases. The fuel pressure in the vicinity of
the tip part therefore increases in accordance with the valve
opening and resultantly the fuel pressure valve closing force
decreases. For the above reason, the fuel pressure valve closing
force is maximum during valve closing and reduces gradually as the
degree of the movement of the valve body 12 toward valve opening
increases.
The behavior of the electromagnetic coil 13 by conduction is
explained hereunder. When the electromagnetic coil 13 is conducted
and an electromagnetic attraction force is generated in the stator
core 14, the movable core 15 is attracted toward the stator core 14
by the electromagnetic attraction force. The electromagnetic
attraction force is also called an electromagnetic force. As a
result, the valve body 12 connected to the movable core 15 operates
for valve opening against the resilient force of the main spring
SP1 and the fuel pressure valve closing force. On the other hand,
when the conduction of the electromagnetic coil 13 is stopped, the
valve body 12 operates for valve closing together with the movable
core 15 by the resilient force of the main spring SP1.
The configuration of the fuel injection control device 20 is
explained hereunder. The fuel injection control device 20 is
operated by an electronic control unit (called ECU for short). The
fuel injection control device 20 includes a control circuit 21, a
booster circuit 22, a voltage detection unit 23, a current
detection unit 24, and a switch unit 25. The control circuit 21 is
also called a microcomputer. The fuel injection control device 20
receives information from various sensors. For example, a fuel
pressure supplied to the fuel injection valve 10 is detected by a
fuel pressure sensor 31 attached to the delivery pipe 30 and the
detection result is given to the fuel injection control device 20
as shown in FIG. 1. The fuel injection control device 20 controls
the drive of the high-pressure pump 40 on the basis of the
detection result of the fuel pressure sensor 31.
The control circuit 21 includes a central processing unit, a
non-volatile memory (ROM), a volatile memory (RAM), and the like
and calculates a requested injection quantity and a requested
injection start time of a fuel on the basis of a load and a machine
rotational speed of an internal combustion engine E. The storage
mediums such as a ROM and a RAM are non-transitive tangible storage
mediums to non-temporarily store programs and data that are
readable by a computer. The control circuit 21: functions as an
injection control unit; tests and stores an injection
characteristic showing a relationship between a conduction time Ti
and an injection quantity Q in the ROM beforehand; controls the
conduction time Ti to the electromagnetic coil 13 in accordance
with the injection characteristic; and thus controls the injection
quantity Q. The control circuit 21 outputs an injection command
pulse that is a pulse signal to command conduction to the
electromagnetic coil 13 and the conduction time of the
electromagnetic coil 13 is controlled by a pulse-on period (pulse
width) of the pulse signal.
The voltage detection unit 23 and the current detection unit 24
detect a voltage and an electric current applied to the
electromagnetic coil 13 and give the detection results to the
control circuit 21. The voltage detection unit 23 detects a minus
terminal voltage of the electromagnetic coil 13. When an electric
current supplied to the electromagnetic coil 13 is intercepted, a
flyback voltage is generated in the electromagnetic coil 13.
Further, in the electromagnetic coil 13, an induced electromotive
force is generated by intercepting the electric current and
displacing the valve body 12 and the movable core 15 in the valve
closing direction. In accordance with the turn-off of the
conduction to the electromagnetic coil 13 therefore, a voltage of a
value obtained by overlapping a voltage caused by the induced
electromotive force to the flyback voltage is generated in the
electromagnetic coil 13. It can accordingly be said that the
voltage detection unit 23 detects the variation of an induced
electromotive force caused by intercepting an electric current
supplied to the electromagnetic coil 13 and displacing the valve
body 12 and the movable core 15 toward the valve closing direction
as a voltage value. Further, the voltage detection unit 23 detects
the variation of an induced electromotive force caused by
displacing the movable core 15 relatively to the valve body 12
after the valve seat 17b comes into contact with the valve body 12
as a voltage value. A valve closing detection unit 54 detects a
valve closing timing when the valve body 12 shifts for valve
closing by using a detected voltage. The valve closing detection
unit 54 detects a valve closing timing for the fuel injection valve
10 in every cylinder.
The control circuit 21 has a charge control unit 51, a discharge
control unit 52, a current control unit 53, the valve closing
detection unit 54, an injection quantity estimation unit 55, and a
current inclination detection unit 56. The booster circuit 22 and
the switch unit 25 operate on the basis of an injection command
signal outputted from the control circuit 21. The injection command
signal is a signal to command a conduction state of the
electromagnetic coil 13 in the fuel injection valve 10 and is set
by using a requested injection quantity and a requested injection
start time. In the present embodiment, the current inclination
detection unit 56 corresponds to a detection unit.
The booster circuit 22 applies a boosted boost voltage to the
electromagnetic coil 13. The booster circuit 22 has a booster coil,
a condenser, and a switching element, a battery voltage applied
from a battery terminal of a battery 102 is boosted by the booster
coil, and the electricity is stored in the condenser. The voltage
of the electric power boosted and stored in this way corresponds to
a boost voltage.
When the discharge control unit 52 turns on a prescribed switching
element so that the booster circuit 22 may discharge electricity, a
boost voltage is applied to the electromagnetic coil 13 in the fuel
injection valve 10. The discharge control unit 52 turns off the
prescribed switching element in the booster circuit 22 when voltage
application to the electromagnetic coil 13 stops.
The current control unit 53 controls on or off of the switch unit
25 and controls the electric current flowing in the electromagnetic
coil 13 by using a detection result of the current detection unit
24. The switch unit 25 applies a battery voltage or a boost voltage
from the booster circuit 22 to the electromagnetic coil 13 in an on
state and stops the application in an off state. The current
control unit 53, at a voltage application start time commanded by
an injection command signal for example: turns on the switch unit
25; applies a boost voltage; and starts conduction. Then a coil
current increases in accordance with the start of the conduction.
When a coil current detection value is detected having reached a
target value Ith (refer to FIGS. 8 and 9) on the basis of a
detection result of the current detection unit 24, the current
control unit 53 turns off conduction by a boosted voltage. In
short, the current control unit 53 controls a coil current so as to
be raised to the target value Ith by applying a boost voltage
through initial conduction. Further, the current control unit 53
controls conduction by a battery voltage so that a coil current may
be maintained at a value lower than the target value Ith after a
boost voltage is applied.
As shown in FIG. 3, an injection characteristic map representing a
relationship between an injection command pulse width and an
injection quantity is classified into a full lift region where an
injection command pulse width is relatively large and a partial
lift region where an injection command pulse width is relatively
small. In the full lift region, the valve body 12: operates for
valve opening until the lift quantity of the valve body 12 reaches
a full lift position, namely a position where the movable core 15
abuts on the stator core 14; and stars operating for valve closing
from the abutting position. In the partial lift region however, the
valve body 12: operates for valve opening in a partial lift state
where the lift quantity of the valve body 12 does not reach the
full lift position, in other words to a position before the movable
core 15 abuts on the stator core 14; and starts operating for valve
closing from the partial lift position.
The fuel injection control device 20, in a full lift region,
executes full lift injection of driving the fuel injection valve 10
for valve opening by an injection command pulse allowing the lift
quantity of the valve body 12 to reach a full lift position.
Further, the fuel injection control device 20, in a partial lift
region, executes partial lift injection of driving the fuel
injection valve 10 for valve opening by an injection command pulse
causing a partial lift state where the lift quantity of the valve
body 12 does not reach a full lift position.
A detection mode of the valve closing detection unit 54 is
explained hereunder in reference to FIG. 4. The graph at the upper
part in FIG. 4 shows a waveform of minus terminal voltage of the
electromagnetic coil 13 after conduction is switched from on to off
and enlargedly shows a waveform of flyback voltage when conduction
of the electromagnetic coil 13 is switched off. The flyback voltage
is a negative value and hence is shown upside down in FIG. 4. In
other words, a waveform of voltage obtained by reversing the
positive and negative is shown in FIG. 4.
The valve closing detection unit 54 detects a physical quantity
having a correlation with an injection quantity actually injected
(actual injection quantity) during partial lift injection. The
valve closing detection unit 54 has a timing detection unit 54a to
detect a valve closing timing by a timing detection mode, an
electromotive force quantity detection unit 54b to detect a valve
closing timing by an electromotive force quantity detection mode,
and a selection switch unit 54c to select and switch either of the
detection modes. The valve closing detection unit 54 cannot detect
a valve closing timing by both of the detection modes
simultaneously and detects a valve closing timing when the valve
body 12 shifts to valve closing by using either of the detection
modes.
Firstly, an electromotive force quantity detection mode is
explained.
Roughly, an electromotive force quantity detection mode is a mode
of detecting a timing (integrated timing) when an integrated value
of induced electromotive force reaches a prescribed quantity as a
physical quantity having a correlation with an actual injection
quantity. A timing when the valve body 12 is actually seated over
the valve seat 17b for valve closing (actual valve closing timing)
and an integrated timing are highly correlated. Then a timing when
the valve body 12 separates actually from the valve seat 17b for
valve opening (actual valve opening timing): is highly correlated
with a conduction start timing; and hence can be regarded as a
known timing. It can therefore be said that, as long as an
integrated timing having a high correlation with an actual valve
closing timing is detected, a period of time spent for actual
injection (actual injection period) can be estimated and eventually
an actual injection quantity can be estimated. In other words, it
can be said that an integrated timing is a physical quantity having
a correlation with an actual injection quantity.
Meanwhile, as shown in FIG. 4, minus terminal voltage varies by
induced electromotive force after the time t1 when an injection
command pulse is turned off. When a detected voltage waveform
(refer to the symbol L1) is compared with a voltage waveform (refer
to the symbol L2) in a virtual case where induced electromotive
force is not generated, it is obvious that, in the detected voltage
waveform, the voltage increases by the induced electromotive force
shown with the oblique lines in FIG. 4. The induced electromotive
force is generated when the movable core 15 passes through a
magnetic field during the period from the start of valve closing
operation to the completion of the valve closing.
Since the change rate of the valve body 12 and the change rate of
the movable core 15 vary comparatively largely and the change
characteristic of a minus terminal voltage varies at the valve
closing timing of the valve body 12, the change characteristic of a
minus terminal voltage varies in the vicinity of the valve closing
timing. That is, the voltage waveform takes a shape of generating
an inflection point (voltage inflection point) at a valve closing
timing. Then a timing of generating a voltage inflection point is
highly correlated with an integrated timing.
By paying attention to such a characteristic, the electromotive
force quantity detection unit 54b detects a voltage inflection
point time as information related to the integrated timing having a
high relation with a valve closing timing as follows. The detection
of a valve closing timing shown below is executed for each of the
cylinders. The electromotive force quantity detection unit 54b
calculates a first filtered voltage Vsm1 obtained by filtering
(smoothing) a minus terminal voltage Vm of the fuel injection valve
10 with a first low-pass filter during the implementation of
partial lift injection at least after an injection command pulse of
the partial lift injection is switched off. The first low-pass
filter uses a first frequency lower than the frequency of a noise
component as the cut-off frequency. Further, the valve closing
detection unit 54 calculates a second filtered voltage Vsm2
obtained by filtering (smoothing) the minus terminal voltage Vm of
the fuel injection valve 10 with a second low-pass filter using a
second frequency lower than the first frequency as the cut-off
frequency. As a result, the first filtered voltage Vsm1 obtained by
removing a noise component from a minus terminal voltage Vm and the
second filtered voltage Vsm2 used for voltage inflection point
detection can be calculated.
Further, the electromotive force quantity detection unit 54b
calculates a difference Vdiff (=Vsm1-Vsm2) between the first
filtered voltage Vsm1 and the second filtered voltage Vsm2.
Furthermore, the valve closing detection unit 54 calculates a time
from a prescribed reference timing to a timing when the difference
Vdiff comes to be an inflection point as a voltage inflection point
time Tdiff. On this occasion, as shown in FIG. 5, the voltage
inflection point time Tdiff is calculated by regarding a timing
when the difference Vdiff exceeds a prescribed threshold value Vt
as a timing when the difference Vdiff comes to be an inflection
point. In other words, a time from a prescribed reference timing to
a timing when a difference Vdiff exceeds a prescribed threshold
value Vt is calculated as the voltage inflection point time Tdiff.
The difference Vdiff corresponds to an accumulated value of induced
electromotive forces and the threshold value Vt corresponds to a
prescribed reference quantity. The integrated timing corresponds to
a timing where the difference Vdiff reaches the threshold value Vt.
In the present embodiment, the voltage inflection point time Tdiff
is calculated by regarding the reference timing as a time t2 when
the difference is generated. The threshold value Vt is a fixed
value or a value calculated by the control circuit 21 in response
to a fuel pressure, a fuel temperature, and others.
In a partial lift region of the fuel injection valve 10, since an
injection quantity varies and also a valve closing timing varies by
the variation of a lift quantity of the fuel injection valve 10,
there is a correlation between an injection quantity and a valve
closing timing of the fuel injection valve 10. Further, since a
voltage inflection point time Tdiff varies in response to the valve
closing timing of the fuel injection valve 10, there is a
correlation between a voltage inflection point time Tdiff and an
injection quantity. By paying attention to such correlations, an
injection command pulse correction routine is executed by the fuel
injection control device 20 and hence an injection command pulse in
partial lift injection is corrected on the basis of a voltage
inflection point time Tdiff.
Secondly, a timing detection mode is explained.
Roughly, an electromotive force quantity detection mode is a mode
of detecting a timing (integrated timing) when an integrated value
of induced electromotive force reaches a prescribed quantity as a
physical quantity having a correlation with an actual injection
quantity. The timing detection unit 54a detects a timing when an
increment of induced electromotive force per unit of time starts
reducing as a valve closing timing.
The timing detection mode is explained hereunder. At a moment when
the valve body 12 starts valve closing operation from a valve
opening state and comes into contact with the valve seat 17b, since
the movable core 15 separates from the valve body 12, the
acceleration of the movable core 15 varies at the moment when the
valve body 12 comes into contact with the valve seat 17b. In the
timing detection mode, a valve closing timing is detected by
detecting the variation of the acceleration of the movable core 15
as the variation of an induced electromotive force generated in the
electromagnetic coil 13. The variation of the acceleration of the
movable core 15 can be detected by a second-order differential
value of a voltage detected by the voltage detection unit 23.
Specifically, as shown in FIG. 4, after the conduction to the
electromagnetic coil 13 is stopped at the time t1, the movable core
15 switches from upward displacement to downward displacement in
conjunction with the valve body 12. Then when the movable core 15
separates from the valve body 12 after the valve body 12 shifts to
valve closing, a force in the valve closing direction that has
heretofore been acting on the movable core 15 through the valve
body 12, namely a force caused by a load by the main spring SP1 and
a fuel pressure, disappears. A load of the sub spring SP2 therefore
acts on the movable core 15 as a force in the valve opening
direction. When the valve body 12 reaches a valve closing position
and the direction of the force acting on the movable core 15
changes from the valve closing direction to the valve opening
direction, the increase of an induced electromotive force that has
heretofore been increasing gently reduces and the second-order
differential value of a voltage turns downward at the valve closing
time t3. By detecting the a timing where the second-order
differential value of a minus terminal voltage becomes maximum by
the timing detection unit 54a, a valve closing timing of the valve
body 12 can be detected with a high degree of accuracy.
Similarly to the electromotive force quantity detection mode, there
is a correlation between a valve closing time from the stop of
conduction to a valve closing timing and an injection quantity. By
paying attention to such a correlation, an injection command pulse
correction routine is executed by the fuel injection control device
20 and thus an injection command pulse in partial lift injection is
corrected on the basis of the valve closing time.
As shown in FIG. 6, an injection time varies in response to a
requested injection quantity. Then in a partial lift region, the
detection range of the electromotive force quantity detection mode
and the detection range W of the timing detection mode are
different from each other. Specifically, the detection range W of
the timing detection mode is located on the side where a required
injection quantity is larger than a reference ratio in the partial
lift region. The electromotive force quantity detection mode covers
from a minimum injection quantity .tau.min to a value in the
vicinity of a maximum injection quantity .tau.max. The detection
range of the electromotive force quantity detection mode therefore
includes the detection range W of the timing detection mode and is
wider than the detection range W of the timing detection mode. The
detection accuracy of a valve closing timing in the timing
detection mode however is superior. In short, the present inventors
have obtained the knowledge that the electromotive force quantity
detection mode has a larger detection range than the timing
detection mode and the timing detection mode has a higher degree of
detection accuracy than the electromotive force quantity detection
mode. On the basis of the knowledge, the selection switch unit 54c
selects and switches either of the detection modes.
The injection quantity estimation unit 55 estimates an actual
injection quantity on the basis of a detection result of the valve
closing detection unit 54. For example, in the case of the timing
detection mode, the injection quantity estimation unit 55 estimates
an actual injection quantity on the basis of a detection result of
the timing detection unit 54a, namely a timing when the
second-order differential value of a minus terminal voltage comes
to be the maximum. Specifically, a relationship among a timing when
a second-order differential value comes to be the maximum, a
conduction time, a supplied fuel pressure, and an actual injection
quantity is stored as a timing detection map beforehand. Then the
injection quantity estimation unit 55 estimates an actual injection
quantity in reference to the timing detection map on the basis of a
detection value of the timing detection unit 54a, a supplied fuel
pressure detected by the fuel pressure sensor 31, and a conduction
time.
Meanwhile, in the electromotive force quantity detection mode for
example, the injection quantity estimation unit 55 estimates an
actual injection quantity on the basis of a detection result of the
electromotive force quantity detection unit 54b, namely a voltage
inflection point time. Specifically, a relationship among a voltage
inflection point time, a conduction time, a supplied fuel pressure,
and an actual injection quantity is stored as an electromotive
force quantity detection map beforehand. Then the injection
quantity estimation unit 55 estimates an actual injection quantity
in reference to the electromotive force quantity detection map on
the basis of a detection value of the electromotive force quantity
detection unit 54b, a supplied fuel pressure detected by the fuel
pressure sensor 31, and a conduction time.
A processor included in the control circuit 21 executes learning
processing that will be explained below. Through the learning
processing, a learning value used at S11 in FIG. 7, namely an
actual injection correction value that is a correction value to
correct a requested injection quantity, is obtained. Specifically,
an actual injection correction value for a requested injection
quantity is calculated for learning on the basis of a deviation
between an actual injection quantity estimated on the basis of a
detection result of the valve closing detection unit 54 and an
injection quantity corresponding to a command conduction time
related to the actual injection, namely a corrected requested
injection quantity. In the present embodiment, the ratio of a
requested injection quantity to an actual injection quantity is
defined as an actual injection correction value. Consequently, when
an actual injection quantity is larger than a requested injection
quantity, the actual injection correction value comes to be a value
smaller than 1 in order to reduce the next requested injection
quantity and, when an actual injection quantity is smaller than a
requested injection quantity, the actual injection correction value
comes to be a value larger than 1 in order to increase the next
requested injection quantity.
Meanwhile, in view of the aforementioned knowledge shown in FIG. 6,
the selection switch unit 54c switches to: a timing detection mode
when a requested injection quantity is equal to or larger than a
reference quantity; and an electromotive force quantity detection
mode when a requested injection quantity is not equal to or larger
than a reference quantity. As a result, the learning is executed:
on the basis of an actual injection quantity estimated by a
detection result of the timing detection unit 54a when a requested
injection quantity is equal to or larger than a reference quantity;
and on the basis of an actual injection quantity estimated by a
detection result of the electromotive force quantity detection unit
54b when a requested injection quantity is not equal to or larger
than a reference quantity.
The current inclination detection unit 56 detects a speed at which
an electric current flowing in the electromagnetic coil 13
increases in accordance with the start of conducting the
electromagnetic coil 13. The current increase speed corresponds to
the inclination of the electric current waveform represented by the
symbol .DELTA.I in the electric current waveforms shown at the
upper stage in either of FIGS. 8 and 9. Specifically, the current
inclination detection unit 56: detects a time required from the
start of conducting the electromagnetic coil 13 until an electric
current reaches a prescribed value; and regards the required time
as a current increase speed. The prescribed value is the target
value Ith stated earlier that is used by the current control unit
53. In other words, the current inclination detection unit 56
detects a time required from the timing of turning on an injection
command pulse until the current detection unit 24 detects that a
coil current has reached the target value Ith.
FIG. 7 is a flowchart showing the procedures through which a
processor included in the control circuit 21 executes a program
stored in a memory included in the control circuit 21 repeatedly in
a prescribed cycle. In the processing of injection control shown in
FIG. 7, firstly at S10, a requested injection quantity is
calculated on the basis of a load and a machine rotational speed of
an internal combustion engine E. At S11, an actual injection
correction value for the requested injection quantity calculated at
S10 is set by using a learning value obtained through the learning
processing described earlier. Although a coefficient value by which
the requested injection quantity is multiplied is set at an actual
injection correction value and the requested injection quantity is
corrected by multiplying the requested injection quantity by the
actual injection correction value in the present embodiment, it is
also possible to: set a deviation between an actual injection
quantity and a requested injection quantity at an actual injection
correction value; and correct the requested injection quantity by
adding the actual injection correction value to or subtracting the
actual injection correction value from the requested injection
quantity.
At S12, a correction coefficient for a temperature characteristic
(temperature characteristic correction coefficient) is set on the
basis of a current increase speed detected by the current
inclination detection unit 56. For example, a relationship between
a current increase speed and a temperature characteristic
correction coefficient is mapped and stored beforehand and a
temperature characteristic correction coefficient is set on the
basis of a current increase speed in reference to the correction
coefficient map. Here, it is also possible to: make a correction
coefficient map beforehand by being associated with a supplied fuel
pressure to the fuel injection valve 10 in addition to the current
increase speed; and set a temperature characteristic correction
coefficient on the basis of a current increase speed and a supplied
fuel pressure in reference to the correction coefficient map.
At S13, an offset correction quantity for a temperature
characteristic is set on the basis of a current increase speed
detected by the current inclination detection unit 56. For example,
a relationship between a current increase speed and a temperature
characteristic offset correction quantity is mapped and stored
beforehand and a temperature characteristic offset correction
quantity is set on the basis of a current increase speed in
reference to the offset correction quantity map. Here, it is also
possible to: make an offset correction quantity map beforehand by
being associated with a supplied fuel pressure in addition to the
current increase speed; and set a temperature characteristic offset
correction quantity on the basis of a current increase speed and a
supplied fuel pressure in reference to the offset correction
quantity map.
At S14, the requested injection quantity calculated at S10 is
corrected by an actual injection correction value, a temperature
characteristic correction coefficient, and a temperature
characteristic offset correction quantity set at S11, S12, and S13.
Specifically, the requested injection quantity is corrected by
multiplying the requested injection quantity by an actual injection
correction value and a temperature characteristic correction
coefficient and adding a temperature characteristic offset
correction quantity to the requested injection quantity.
Here, an injection characteristic map representing a relationship
between a conduction time and an injection quantity is stored in
the control circuit 21 beforehand. Then at S15, a conduction time
corresponding to the corrected requested injection quantity
calculated at S14 is calculated in reference to the injection
characteristic map. As the injection characteristic map, a
plurality of maps are stored in response to supplied fuel pressures
detected by the fuel pressure sensor 31 and a conduction time is
calculated in reference to an injection characteristic map
corresponding to a supplied fuel pressure of every moment. At S16,
the electromagnetic coil 13 is conducted on the basis of a
conduction time calculated at S15. Specifically, a pulse width of
an injection command pulse is set as the length of a calculated
conduction time.
Meanwhile, the control circuit 21 during the processes of S12 and
S13 corresponds to a correction value calculation unit to calculate
a correction value for a requested injection quantity on the basis
of a current increase speed. In particular, the control circuit 21
during the process of S13 corresponds to an offset correction
quantity calculation unit to calculate an offset correction
quantity as a correction value and the control circuit 21 during
the process of S12 corresponds to a correction coefficient
calculation unit to calculate a correction coefficient as a
correction value. Further, the control circuit 21 during the
process of S15 corresponds to a conduction time calculation unit to
calculate a conduction time of the electromagnetic coil 13
corresponding to a requested injection quantity.
Technical significance of correcting a requested injection quantity
by a temperature characteristic offset correction quantity and a
temperature characteristic correction coefficient is explained
hereunder in reference to FIGS. 8, 9, and 10.
An increase speed of a coil current immediately after the start of
conduction varies in response to a temperature of the
electromagnetic coil 13. As a result, an injection characteristic
changes as stated earlier. In FIGS. 8 and 9, the solid lines show
electric current waveforms and injection rate waveforms during
ordinary temperature and the dotted lines show electric current
waveforms and injection rate waveforms during high temperature. The
injection rate means a quantity injected through the injection hole
17a per unit of time. Then a value obtained by integrating
injection rates, namely an area surrounded by an injection rate
waveform and a horizontal axis, shows an injection quantity during
one time valve opening.
In the example shown in FIG. 8, an injection quantity is smaller
during high temperature than during ordinary temperature. The
reason is that it takes time to increase an attraction force to the
extent of starting valve opening operation because the inclination
.DELTA.I of an electric current waveform reduces during high
temperature and hence a valve opening start time delays. On the
other hand, in the example shown in FIG. 9, the conduction time Ti
is slightly longer than the case of FIG. 8. Then in the example of
FIG. 9, an injection quantity is larger during high temperature
than during ordinary temperature. The reason is that an energy loss
caused by the generation of eddy current is small because the
inclination .DELTA.I of an electric current waveform reduces during
high temperature and the valve opening speed of the valve body 12
is high. For the reason, although a valve opening start time delays
during high temperature, since the valve opening speed is high, if
a conduction time Ti is equal to or longer than a prescribed time,
the area of an injection rate waveform increases in comparison with
during low temperature and an injection quantity increases.
In short, whereas a valve opening start time delays and an invalid
injection period from the start of conduction to the start of valve
opening operation increases during high temperature, the loss of
electric energy supplied to the electromagnetic coil 13 reduces
during the high temperature. As a result, as shown in FIG. 10, when
a conduction time Ti is equal to or longer than a prescribed time,
an injection quantity is larger during the high temperature shown
by the long dashed short dashed line and the dotted line than
during the ordinary temperature shown by the solid line. When a
conduction time Ti is shorter than a prescribed time however, an
injection quantity is smaller during the high temperature shown by
the long dashed short dashed line and the dotted line than during
the ordinary temperature shown by the solid line. Here, FIG. 10 is
an example of the case where a supplied fuel pressure is 20 MPa and
the electric resistance of the electromagnetic coil 13 is larger:
by 0.25.OMEGA. in the case of the dotted line than in the case of
the solid line; and by 0.75.OMEGA. in the case of the long dashed
short dashed line than in the case of the solid line.
Here, an injection characteristic line L includes a first region A1
where the inclination of the injection characteristic line L
increases gradually in proportion to the increase of a conduction
time and reaches a prescribed inclination and a second region A2,
the second region being a region on the side where the conduction
time is longer than the first region A1, where the inclination of
the injection characteristic line L forms a constant straight line.
For example, the inclination of the injection characteristic line L
during ordinary temperature in the second region A2 is set at
.DELTA.Q and the inclination of the injection characteristic line
La during high temperature in the second region A2 is set at
.DELTA.Qa. The ratio of the inclination .DELTA.Qa during high
temperature to the inclination .DELTA.Q during ordinary temperature
corresponds to a temperature characteristic correction coefficient.
As stated earlier, because an energy loss reduces as a temperature
rises, as shown in FIG. 10, the inclination .DELTA.Qa during high
temperature is larger than the inclination .DELTA.Q during ordinary
temperature. That is, a temperature characteristic correction
coefficient is set at a higher value as a temperature rises.
Then since the inclination of an injection characteristic line in
the second region and a current increase speed are highly
correlated with each other, a relationship between the inclination
of an injection characteristic line in the second region and a
current increase speed can be obtained beforehand by experiment and
the inclination of the injection characteristic line is used as a
temperature characteristic correction coefficient. Otherwise, a
temperature characteristic correction coefficient is obtained by
adding a prescribed constant to the above inclination or
multiplying the above inclination by a prescribed coefficient. The
correction coefficient map stated earlier therefore is made on the
basis of the above experimental result.
Further, the injection characteristic line in the second region A2
has the shape of a straight line having a constant inclination and
the value of the conduction time when the injection quantity is
zero on a virtual straight line Lv formed by extending the straight
line is defined as a virtual time Tv. The virtual time Tv
corresponds to the invalid injection period stated earlier. A value
obtained by multiplying a time difference Ta between a virtual time
Tv during ordinary temperature and a virtual time Tva during high
temperature by a prescribed coefficient corresponds to a
temperature characteristic offset correction quantity. As stated
earlier, because an invalid injection period increases as a
temperature rises, as shown in FIG. 10, the virtual time Tva during
high temperature is longer than the virtual time Tv during ordinary
temperature. That is, a temperature characteristic offset
correction quantity is set at a higher value as a temperature
rises.
Then since a virtual time Tva that is an invalid injection period
and a current increase speed are highly correlated with each other,
a relationship between a virtual time Tva and a current increase
speed can be obtained beforehand by experiment and a temperature
characteristic offset correction quantity is calculated on the
basis of the virtual time Tva. For example, the difference of the
virtual time Tva from a virtual time Tv during ordinary temperature
is used as a temperature characteristic offset correction quantity.
Otherwise, a temperature characteristic offset quantity is obtained
by adding a prescribed constant to the above difference or
multiplying the above difference by a prescribed coefficient. The
offset correction quantity map stated earlier therefore is made on
the basis of the above experimental result.
In short, a first phenomenon of reducing energy loss as a
temperature rises is reflected on a temperature characteristic
correction coefficient and a second phenomenon of increasing an
invalid injection period as a temperature rises is reflected on a
temperature characteristic offset correction quantity. The first
phenomenon is to increase an injection quantity as a temperature
rises and the second phenomenon is to reduce an injection quantity
as a temperature rises. Such two kinds of phenomena conflicting
with each other are sorted into a temperature characteristic offset
correction quantity and a temperature characteristic correction
coefficient respectively and then reflected as correction
values.
As explained above, in the present embodiment, the current
inclination detection unit 56 to detect a current increase speed
during partial lift injection, a correction value calculation unit
at S12 and S13, and a conduction time calculation unit at S15 are
provided. The correction value calculation unit calculates a
correction value for a requested injection quantity on the basis of
a detected current increase speed and the conduction time
calculation unit calculates a conduction time during partial lift
injection on the basis of the requested injection quantity
corrected by the correction value. Then since the change of an
injection characteristic responding to a temperature is highly
correlated with a current increase speed, according to the present
embodiment, control can be executed by a conduction time suitable
for an injection characteristic varying in response to a
temperature during partial lift injection. A fuel injection
quantity in partial lift injection therefore can be controlled with
a high degree of accuracy.
In the present embodiment further, the correction value calculation
unit has an offset correction quantity calculation unit at S13 and
a correction coefficient calculation unit at S12. The offset
correction quantity calculation unit calculates an offset
correction quantity to correct a requested injection quantity by
adding the offset correction quantity to or subtracting the offset
correction quantity from the requested injection quantity on the
basis of a current increase speed. The correction coefficient
calculation unit calculates a correction coefficient to correct a
requested injection quantity by multiplying the requested injection
quantity by the correction coefficient on the basis of a current
increase speed. According to this, as described earlier in
reference to FIGS. 8 to 10, two kinds of phenomena are sorted into
a temperature characteristic offset correction quantity and a
temperature characteristic correction coefficient respectively and
then reflected as correction values. As a result, a fuel injection
quantity in partial lift injection can be controlled with a yet
higher degree of accuracy. In particular, although an injection
characteristic varies largely depending on the kind of the fuel
injection valve 10, even when an injection characteristic varies
largely by the difference of machine types, control can be executed
likewise with a high degree of accuracy and the robustness of
control against the difference of injection characteristics by
machine types can be improved.
In the present embodiment furthermore, the correction coefficient
calculation unit calculates a temperature characteristic correction
coefficient on the basis of an inclination .DELTA.Qa of an
injection characteristic line La in a second region A2 estimated
from a correlation with a current increase speed. As a result, the
degree of the first phenomenon of reducing energy loss as a
temperature rises stated earlier is reflected on a temperature
characteristic correction coefficient and hence the accuracy of
correcting a requested injection quantity can be improved.
In the present embodiment yet further, a value of a conduction time
when an injection quantity is zero on a virtual straight line Lv
formed by extending the straight line of an injection
characteristic line L in a second region A2 is defined as a virtual
time Tv. Then an offset correction quantity calculation unit
calculates a temperature characteristic offset correction quantity
on the basis of a virtual time Tv estimated from a correlation with
a current increase speed. As a result, the degree of the second
phenomenon of increasing an invalid injection period as a
temperature rises stated earlier is reflected on a temperature
characteristic offset correction quantity and hence the accuracy of
correcting a requested injection quantity can be improved.
In the present embodiment moreover, the current inclination
detection unit 56 obtains a current increase speed by detecting a
time required from the start of conducting the electromagnetic coil
13 until an electric current flowing in the electromagnetic coil 13
reaches a prescribed value (for example, a target value Ith).
According to this, a current increase speed is obtained by using
information that is used for the current control unit 53 to control
the conduction state of the electromagnetic coil 13 and is
information on whether or not a coil current has reached a target
value Ith. As a result, a current increase speed can be obtained
without using a circuit used exclusively for calculating a
correction value and hence the circuit configuration of a fuel
injection control device can be simplified.
Here, as stated earlier, the timing detection mode and the induced
electromotive force detection mode have advantages and
disadvantages respectively. It is desirable therefore to detect a
valve closing timing simultaneously by both of the detection modes.
In order to make it possible to execute both of the detection modes
simultaneously however, the processing capability of the control
circuit 21 has to be enhanced and the implementation scale of the
fuel injection control device 20 may increase undesirably. In view
of this point, the valve closing detection unit 54 according to the
present embodiment has the timing detection unit 54a of the timing
detection mode, the electromotive force quantity detection unit 54b
of the induced electromotive force detection mode, and the
selection switch unit 54c to select and switch either of the
detection modes. Consequently, the valve closing detection unit 54
can switch so as to exhibit the advantages of both of the modes and
can be downsized further than a configuration of executing both of
the modes simultaneously.
(Other Embodiments)
The embodiment of the present disclosure has been described with
reference to specific examples. However, the present disclosure is
not limited to these specific examples. That is, ones obtained by
modifying the design of these specific examples as appropriate by a
person skilled in the art are also included in the scope of the
present disclosure as long as they have the characteristics of the
present disclosure.
In the first embodiment stated above, the current inclination
detection unit 56 obtains a current increase speed by detecting a
time from the start of conducting the electromagnetic coil 13 until
a coil current reaches a prescribed value. In place of the
detection mode, it is also possible to obtain a current increase
speed by detecting a current increase quantity from the start of
conducting the electromagnetic coil 13 until a prescribed time
lapses.
In the first embodiment stated above, a temperature characteristic
correction coefficient and a temperature characteristic offset
correction quantity are calculated individually on the basis of a
current increase speed and a requested injection quantity is
corrected by the temperature characteristic correction coefficient
and the temperature characteristic offset correction quantity
respectively. On the other hand, it is also possible to: calculate
either a correction coefficient for multiplication or a correction
quantity for addition on the basis of a current increase speed; and
correct a requested injection quantity by a calculated correction
coefficient or correction quantity.
Although the fuel injection valve 10 is configured so as to have
the valve body 12 and the movable core 15 individually in the first
embodiment stated earlier, the fuel injection valve 10 may also be
configured so as to have the valve body 12 and the movable core 15
integrally. If they are configured integrally, the valve body 12 is
displaced together with the movable core 15 in the valve opening
direction and shifts to valve opening when the movable core 15 is
attracted.
Although the fuel injection valve 10 is configured so as to start
the shift of the valve body 12 at the same time as the start of the
shift of the movable core 15 in the first embodiment stated
earlier, the fuel injection valve 10 is not limited to such a
configuration. For example, the fuel injection valve 10 may be
configured so that: the valve body 12 may not start valve opening
even when the movable core 15 starts shifting; and the movable core
15 may engage with the valve body 12 and start valve opening at the
time when the movable core 15 moves by a prescribed distance.
Although the voltage detection unit 23 detects a minus terminal
voltage of the electromagnetic coil 13 in the first embodiment
stated above, a plus terminal voltage or a voltage across terminals
between a plus terminal and a minus terminal may also be
detected.
In the first embodiment stated above, the valve closing detection
unit 54 detects a terminal voltage of the electromagnetic coil 13
as a physical quantity having a correlation with an actual
injection quantity. Then the injection quantity estimation unit 55
estimates an actual injection quantity by estimating a valve
closing timing on the basis of a waveform representing the change
of the detected voltage. In contrast, an actual injection quantity
may be estimated also by detecting a supplied fuel pressure as a
physical quantity having a correlation with the actual injection
quantity and estimating a valve closing timing on the basis of a
waveform representing the change of the detected fuel pressure.
Otherwise, an actual injection quantity may be estimated also on
the basis of a waveform representing the change of an engine speed
by detecting the engine speed as a physical quantity having a
correlation with the actual injection quantity.
The functions exhibited by the fuel injection control device 20 in
the first embodiment stated earlier may be exhibited by hardware
and software, those being different from those stated earlier, or a
combination of them. The control device for example may communicate
with another control device and the other control device may
implement a part or the whole of processing. When a control device
includes an electronic circuit, the control device may include a
digital circuit or an analog circuit including many logic
circuits.
While the present disclosure has been described with reference to
embodiments thereof, it is to be understood that the disclosure is
not limited to the embodiments and constructions. The present
disclosure is intended to cover various modification and equivalent
arrangements. In addition, while the various combinations and
configurations, other combinations and configurations, including
more, less or only a single element, are also within the spirit and
scope of the present disclosure.
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